The correct approach would be to contact the firewall vendor and get them to reclassify the site in their blacklists - then it gets fixed for everyone using that firewall. The existing classification may relate to the domain's earlier life.

I actually have this issue (and I'm a moderator!) and it does get rather annoying trying to deal with games questions (only way I can get to them is through the iPhone while I am at work, otherwise they have to wait).

It was rather easy to convince my boss to whitelist stackoverflow because it was actually programming related. I don't think I would have the same luck asking him to whitelist superuser.